The present invention relates to a sample handling system for an optical monitoring system, and more particularly, to an automated sample handling system for an optical evaluation instrument which includes optical monitoring means for monitoring changes in optical characteristics of a reaction volume in a reaction well of a cuvette when the cuvette is positioned in the optical path of the optical monitoring means.
Automated sample handling systems for optical evaluation instruments are known which automatically dispense patient fluid samples, such as blood plasma, along with reagents and other additives, into the reaction well of a cuvette which is then automatically positioned in the optical path between a light source and a detector for monitoring changes in the optical characteristics in the reaction volume of the cuvette as the reaction is allowed to progress over time. Such instruments are useful in the field of biochemical analysis for measuring blood plasma coagulation time and performing factor and other chromogenic assays and related analyses.
An automated sample handling system in an optical evaluation system of this type is described by Nelson L. Alpert, Ph.D., in the Spotlight section of "CIS", a publication by Clinical Instruments Systems, Inc., Volume 9, number May, 5, 1988, pages 1 to 7. The system described by Alpert is based upon principles of centrifugal analysis whereby patient plasma samples and reagents are automatically dispensed into radial chambers of a rotor. The chambers serve both as reaction vessels and as photometric cuvettes. The cuvettes spin through the optical path of a fixed photometer. An optical beam illuminates each cuvette from beneath the rotor and a detector above the rotor collects the light signals from each of the cuvettes in sequence. The optical data are collected and analyzed by the system's computer.
In this system, the automatic dispensing of samples and reagents is accomplished by a single probe arm which has sample and reagent probes. At the beginning of a run, the probe arm rotates to aspirate a sample on a sample tray which accommodates 20 sample cups, one of which is reserved for a calibration plasma or a normal pool sample, and a second for diluent. This leaves room for as many as 18 samples. The rotor likewise has 20 reaction vessels. After aspirating a sample, the probe arm rotates to a reagent reservoir for a test programmed for the sample just aspirated and aspirates a reagent from the reservoir. There are three reagent reservoirs each comprised of a reagent cup which are maintained at about 15.degree. C. The probe arm is next positioned over a reaction vessel in the rotor to dispense both the sample and reagent into the reaction vessel. After a washing process the probe arm repeats the sequence for dispensing sample and reagent into respective reaction vessels until all of the reaction vessels for the particular run are loaded. The rotor is then spun up and the reactants in each radial pathway are spun to a chamber near the circumference of the rotor where the samples spin through the optical path of the photometer. The analytical time after a rotor receives samples and reagents is the same whether a single sample is run singly or in duplicate or the rotor is completely filled with samples. That is, a whole batch of up to 18 samples is analyzed in the same time as a single sample.
While the above-described system provides a certain amount of automation and flexibility to the handling of samples in an optical evaluation instrument, it still has a number of drawbacks. To begin with, the plasma, which is prepared in a separate centrifugation process, must first be transferred from the centrifugated test tube into a sample cup of the sample tray. When the centrifugated test tube comprises an evacuated sample collection tube sealed by a septum, which is now common, this requires either removing the septum or piercing the septum and aspirating a desired amount of plasma out of the collection tube and then dispensing the aspirated plasma into a sample cup of the sample tray. This must be done for each patient plasma sample loaded into the sample tray. This process poses contamination problems, both to the patient samples and to the clinical worker performing the transfer process. It would therefore be preferable if a sample handling system could be designed to eliminate the above-described transfer process by incorporating a mechanism which could remove a patient plasma sample from an evacuated and spun down test tube containing a patient's blood plasma with the septum intact and transfer the patient plasma sample directly to the reaction well of a cuvette without human intervention.
Another drawback of the above-described system is its limited throughput. The rotor only contains 20 reaction vessels, and only a maximum of 18 of these reaction vessels can be used for patient samples. Additionally, only one type of test may be performed on any one run of the rotor. It often occurs, therefore, that some of the available reaction vessels remain unused on a given run. Further, an operator must program the instruments' computer with the identification of each sample and the test to be performed, which further adds to the total analysis time.
A further drawback of the above-described system is that it essentially requires the attendance of a full-time operator. Because the system only runs a maximum of 18 patient samples during any one run, an operator must be present at the conclusion of each run, which may take anywhere from approximately three to eleven minutes, depending on the test being performed, to replace the sample tray with a new sample tray and set the machine up for the next run. It would be desirable to have a sample handling system with equivalent or better throughput of patient samples with walk-away automation on the order of one or more hours, thereby freeing the operator to perform other tasks.
Yet, another drawback of the above-described system is that it can accommodate a relatively limited number reagents at any one time and further, only the reagents are temperature controlled. The lack of temperature control for the patient samples provides an inherent limitation on the number of samples that can be run at any one time since the patient samples must be kept cool just prior to the analysis, at which time the patient samples must be brought up to body temperature.